Master's Defense: Markus Nygaard Pedersen

Understanding the Gatemon

The transmon is one of the most successful designs for superconducting qubits and is used extensively by for example IBM to build their quantum computers. The disadvantage of the transmon is that to tune its frequency we need to introduce a SQUID. The gatemon is an interesting alternative because it offers the possibility of having a tunable qubit without the need of an external magnetic flux. Gatemons get around the use of magnetic fields by introducing a semiconductor into the circuit gives us control of the frequency through controlling the transmission. Unfortunately, when experimentally tested these qubits they perform significantly worse than current theory predicts. In this thesis I numerically solve both the current Hamiltonian for a SNS junction and an alternative Hamiltonian modelling a quantum point contact.  Comparisons of these models indicates that in some regimes the gatemon is more accurately modelled as a quantum point contact than a SNS junction and this might be the reason that the experimental values a worse then the current theory.